The present invention relates to a solar cell system for direct conversion of solar energy to electricity. During the recent years this technique has been widely developed, the cell structures being both cheaper and more effective, and besides, they have become more easily applicable, e.g. in being delivered as a reeled web for mounting in desired sizes on suitable supports. Thereby, real solar cell panels may be built up by local manufacturers or contractors for mounting of the panels on power station areas or on roof or wall areas of buildings, where the panels can be joined so as to cover large areas.
A typical panel size is some xc2xd-1 square meter, e.g. with dimensions 0.5xc3x971 m. Such panels may hold 30-40 solar cells which, when connected in series, may provide a working voltage of 14-18 Volts by direct incidence of the sunlight, this being suitable for the charging of 12 V battery systems. For this purpose the panels may be connected in parallel, but of course they can also be connected in series for generation of a higher voltage. This can be determined in detail for each individual system, all according to the available number of panels.
The panels are mounted most efficiently with equatorially directed angle of incident, i.e. facing south on the northern hemisphere, and with an inclination adjusted according to the relevant latitude such that the average sun in fall can be maximum. In power parks and on flat building roofs this can be achieved by means of suitable carrier structures. In connection with buildings there may sometimes be ideal conditions on inclined roofs facing south, but otherwise it may be fully acceptable to use a less optimal mounting base, e.g. a less optimally inclined roof or even a vertical building wall, inasfar as from a constructional point of view it will be cost saving if the relevant surface can be used for supporting the panels in a direct manner, without the use of carrier structures. It is then possible and also practised to arrange solar cell panels in an architectonically acceptable manner as facade covering units or e.g. as vertical balcony walls.
The invention is based on the consideration that there are certain building parts which, with full architectonical accept, may appear with pronounced slanting orientation, viz. sun shading lamellae mounted outside windows with strong sun infall. These lamellae do not constitute real building faces, but it will be appreciated that they are very well suitable as supports for a solar cell system. Hereby, the traditional conception of solar cell panels as independent, concentrated plate elements should be left behind, as instead elongate and relatively narrow carriers are used for the purpose, e.g. with a width of only 10-20 cm and moreover of such a type which, at the outset, also serves a different purpose, viz. sun shading. These relatively narrow lamellae are well suited as carriers for strips of the said solar cell web material on their outside, as the cells of the material are easily arranged in such a manner that they can be commutated from widely spaced areas and thus generate a desired voltage anyhow. Alternatively, parallel rows of solar cells may be mutually connected at one end, whereby they can be commutated in closely juxtaposed points at the other end.
Apart from any required adaptation of the width of the solar cell web, should it not simply be cuttable into a required smaller width, the invention involves some special circumstances of electrical, mechanical and thermal nature, respectively:
1: COMMUTATION:
In conventional panel systems it is possible to use internal, hidden and factory or workshop mounted series and parallel connections, such that the entire system may appear with a single connector terminal. With the invention it is to be envisaged that it may be required to make extensive use of external wirings and terminations made in situ in conjunction with the mounting work. The lamella technique itself, with lamellae and associated carrier systems, is independently highly developed, and with the invention it is highly undesired to introduce principal modifications in these mechanical systems. As the lamellae extend in parallel and with mutual spacing it will, in practice, be indispensable that wires should be mounted across and, optionally, along these gaps, and special commutation devices should be provided, preferably to be held by the lamellae themselves.
The proper solar cell material will typically be electrically terminated by one or two projecting wires at opposite ends or at one same end of the solar cell strip, respectively, these wires just as typically consisting of flat conductors enclosed between cover sheets endwise projecting from the cell strip. For commutating these conductors, according to the invention, the outer sheet layer can be cut away in local areas above the conductors, while in a nearby area a hole is punched through both the sheet strip and the lamella itself for forming a socket hole, in which there is mounted a wired commutation block provided with one or two contact portions to abut the respective, exposed conductor area or areas a safe abutment being ensured by mechanically clamping together the commutation block and a holding part on the other side of the lamella. Such a mounting can be made in situ, and for the connection of the solar cell strips in series or in parallel across a common end area of the lamellae it is possible to use pre-prepared wire connected commutation blocks with a wire length adapted to the distance between the lamellae, such that the electrical connection work can be reduced to a minimum.
Also, it is thus achievable in a simple manner that the fitters should not be particularly careful for observing a natural requirement of the lamina construction as a whole be kept electrically insulated from the solar cell system. Moreover, the commutation blocks may be designed such that in addition to being insulating they can also be effectively covering the commutation areas, whereby these remain fully protected against corrosion.
2: APPLICATION OF CARRIER STRUCTURE:
The said already highly developed carrier structures for the lamellae will be applicable not only in connection with sun shading systems, but also in general on building surfaces, e.g. building walls and flat roofs or for that sake on pitched roofs, the inclination of which only is not optimum for solar cell panels at the particular place. The carrier structures, including the lamellae themselves, are developed to a high degree of standardization at low costs, and since the lamellae will be perfect carriers for the thin and light cell web material, they are advantageously usable as solar cell panels practically anywhere.
This will or may result in a noticeable change in the technical/architectonical look of the relevant mounting surfaces. Traditionally, the said relatively large, inclined solar cell panels have been mounted in rows with correspondingly large spacings on horizontal surfaces, whereby the surface will visually appear with a pronounced xe2x80x98oblique panelxe2x80x99 structure. With the invention the corresponding oblique panels will be noticeably less projecting, without having reduced capacity because of their higher number. The relevant surface, which may also be a vertical building surface, may then be laid out with a smoothened appearance. It will still be xe2x80x98toothedxe2x80x99, but not more than might well be aimed at by an architectonical decoration of a non-technical character. The look, therefore, will be much more acceptable than in case of conventional solar panels, and with the use of the said specialized carrier structures the installation will even be advantageous with respect to costs. Additionally, due to its smaller modular size in one main direction, viz. across the lamellae, and a less critical modular size in the other main direction, viz. along the lamellae, the installation can more easily be brought to cover areas with irregular boundaries, e.g. in connection with windows in a building wall. It will be another concept that according to the starting point of the invention there may also be mounted solar cell strips on sun shading lamellae provided on a carrier structure mounted above the windows, projecting more or less perpendicularly from the vertical building wall.
Usually, the carrier structures are made up as a series of parallel, light profiles of aluminium which, with the use of suitable mounting fittings, are fastened to the underlying building surface, normally outwardly projecting therefrom; the profiles have profiled grooves in which they receive foot portions of respective rows of lamella holders of plastics, these carrying the lamellae, which extend across the said profiles, solely by a resilient clamping action. The entire system is light and simple due to the relative littleness of the individual lamellae, so the construction will be ideal also in the present connection, no matter whether a given system should additionally serve a sun shading purpose.
In the relevant connection, the use of plastic holders is ideal in that these holders will automatically form an electrical insulation between the single lamellae and the carrier construction, whereby an unintentional electrical leakage between a solar cell strip and a lamella will be kept isolated to the particular lamella.
3: THERMAL CONDITIONS:
The said known lamella systems are, as mentioned, made with lamellae of aluminium, which in the present connection is of particular relevance, such that according to the invention it is highly advantageous to use that kind of lamellae and therewith also the related carrier structures. In this respect the invention builds on the insight that the normally darkcoloured solar cell elements are naturally liable to be heated strongly by the sun rays and that the efficiency of the solar cells decreases by increasing temperature. For the invention, therefore, it is important to consider a cooling of the cell elements, which may well, in sunshine, adopt a temperature of 60-80xc2x0 C., with an associated efficiency decrease of near 10% relative to normal ambient temperatures. In this connection it is of noticeable effect that the element supporting structure is of the well heat conducting aluminium and that the same structure appears in open air surroundings in connection with the relevant carrier structure, as the air may then act cooling on the solar cell elements not only at the outside thereof, but also via the free underside of the associated carrier plate of relatively thin aluminium.
As far as this aspect is concerned it will be advantageous to make use of lamellae having their rear sides profiled with projecting cooling ribs or, themselves, being profiled with interior channels for cooling water. In the latter case the cooling water will be heated by the sun, such that it will additionally applicable in an associated heat pump system for further increase of the efficiency of the system as a whole. The water should not be heated to such a degree that it loses a reasonable cooling effect, but optionally a further heating may be arranged in aftercoupled solar heat collectors for that purpose. Even for that purpose it could be possible to use the said lamellae, which should then only be heat insulated at the cold side.
4: REFLECTION:
Usually, the standard lamellae are mounted rowwise, in suitably inclined positions and with a relatively small mutual distance. This pattern will also be particularly relevant for the invention, when the lamellae are made of aluminium, because the light and smooth rear lamella surfaces will reflect diffuse light against the solar cells on the respective neighbour lamellae, this contributing measurably to the efficiency of the cells.
5: FIXATION:
With the invention it is found desirable to make use of a solar cell material of the thin film type, already for ensuring that the added material shall not influence the calculation basis for the entire lamella screen construction. The thin film should be effectively weather protected, and this can be achieved by enclosing the film between cover sheets of a suitable plastics material, joined face to face outside the edges of the thin film. The front side sheet may advantageously consist of Teflon, whichxe2x80x94unlike glassxe2x80x94has no tendency to collect dust on its surface, while the rear sheet may be of the same or another, optionally non-transparent material, which should preferably be fixable directly to the lamella front sides.
When the lamellae consist of extruded aluminium it will be relatively simple to provide the modification of the lamellae being profiled with flange portions for receiving the opposite edges of the pliable and strip shaped solar cell film laminate, whereby already this may condition a fully sufficient fixation of the sheet strip.
A preferred solution, however, is to avoid such a modification and to secure the sheet strip directly to the front side of the lamella. This is easily achievable with the use of a suitable glue, e.g. of the EVA type with thermal actuation or so-called contact glue. It is a further possibility that the edge areas of the cover sheet strips as projecting beyond the edges of the solar cell strip can be secured to the lamella surfaces by a milling operation, again in particular when the lamellae consist of aluminium. Both hereby and with the use of gluing it may be possible to avoid the rear cover sheet strip, if or when it is possible to ensure a tight enclosure of the solar cell strip solely by the use of the outer cover strip. This will further have the advantageous effect that the rear cover sheet disappears as a heat insulating layer between the solar cell strip and the front side of the aluminium lamellae, whereby the desired cooling is promoted.